linux-kernel - Re: [PATCH] x86_64: Add memcpy32

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Date:	Tue, 16 Sep 2014 20:59:03 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	"Subhransu S. Prusty" <subhransu.s.prusty@...el.com>,
	hpa@...or.com, tglx@...utronix.de, mingo@...hat.com,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64: Add memcpy32_toio to write to PCI MMIO

On Tue, Sep 09, 2014 at 10:01:18AM +0200, Clemens Ladisch wrote:
> Subhransu S. Prusty wrote:
> > This is needed because the hardware
> 
> Which hardware?  Every x86-64 CPU ever built by AMD, Intel, and VIA?
Baytrail and few other SoCs
> 
> > does not support 64-bit moveq insructions while writing to PCI MMIO.
> 
> > +#ifndef CONFIG_X86_64
> > +#define MEMCPY_TOIO memcpy_toio
> > +#else
> > +#define MEMCPY_TOIO memcpy32_toio
> > +#endif
> 
> This does not change any code that uses memcpy_toio().
So the devices cant do 64bit memcpy_toio so we are forced to use 32bit
copies only. This given us such an option
> 
> > +	for (i = 0; i < count/sizeof(u32); i++)
> > +		writel(*src_32++, dst_32++);
> 
> This breaks when count is not a multiple of four.
Ah yes, we can fix that

-- 
~Vinod

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